1. Field of the Invention
The present invention relates to a method for manufacturing a fine structure with the use of an imprint due to a mold having an uneven pattern.
2. Description of the Related Art
As for the method for manufacturing the fine structure, a technique referred to as a nanoimprint method is described in S. Y. Chou et al., “Nanoimprint lithography”, J. Vac. Sci. Technol. B 14(6), November/December 1996, pp 4129-4133. The method described in this literature will be described below with reference to FIGS. 4A to 4D. Firstly, a resist 42 is applied on a surface of a substrate 41 (FIG. 4A). The substrate 41 is heated to a glass transition point temperature or higher of the resist 42, and a mold 43 having a desired uneven pattern formed thereon is pressed onto the softened resist 42 by heating. (FIG. 4B). The temperature of the substrate 41 is decreased to the glass transition temperature of the resist 42 or lower, in a state in which the mold 43 is pressed into the resist 42, and after that, the mold 43 is released from the resist 42 (FIG. 4C). At this time, a residual film 44 of the resist remains in a region in which the resist has been pressed by a salient pattern portion of the mold 43. The residual film 44 of the resist is usually removed, for instance, by ECR (Electron Cyclotron Resonance) etching and the like. By the above described etching, a desired resist pattern can be obtained (FIG. 4D).
Furthermore, a method for forming a pattern by irradiating a photo-curable resin with a light in a state in which a quartz mold is pressed onto the photo-curable resin and curing the photo-curable resin is described in T. Bailey et al., “Step and flash imprint lithography: Template surface treatment and defect analysis”, J. Vac. Sci. Technol. B 18(6), November/December 2000, pp. 3572-3577. In this case, an etched layer is formed on the substrate beforehand, and a residual film of the photo-curable resin and the etched layer are etched by plasma etching, while using a pattern which has been formed by an imprint as a mask. This method is generally referred to as a photo imprint, and shows an effect of reducing the misalignment of the pattern, because of not needing to increase the temperature of the substrate to a high temperature by using the photo-curable resin.
A conventional imprint method is a mechanical processing method for a resist, so a residual film of the resist is formed in a region of having been pressed by the mold, as in the above described example. This residual film of the resist needs to be removed by a technique such as dry etching. For instance, U.S. Pat. No. 6,334,960 describes a method for removing the residual film (residual material) remaining there after the imprint operation, by exposing the residual film under an environment of an argon ion flow, a fluoride-containing plasma, a reactive ion etching gas or a mixture thereof.
In addition, Japanese patent Application Laid-Open No. 2003-272998, Japanese patent Application Laid-Open No. 2004-304097 and Japanese patent Application Laid-Open No. 2005-354017 describe the following imprint method. Firstly, a light-shielding film or a light-shielding portion is formed on a projecting portion of a quartz mold, and the photo-curable resin is selectively irradiated with an irradiation light in a state in which the mold is pressed onto the photo-curable resin. After this, the residual film at a projecting portion of the mold having the light-shielding film is removed by developing the photo-curable resin, and consequently the pattern is imprinted.
However, when the residual film of the resist is removed by the technique such as dry etching as is described in U.S. Pat. No. 6,334,960, it is considered that the shape of the resist pattern is deteriorated or the dimensional controllability is deteriorated like a supposed figure illustrated in FIG. 4D. In other words, a pattern shape (dotted line portion in FIG. 4D) having existed before the dry etching step retreats due to etching. In order to remove the residual film of the resist while retaining a necessary line width and shape of a pattern as much as possible, an etching method having a high anisotropy has been employed, which has caused a problem of increasing an etching treatment period of time. These problems become more remarkable as a desired pattern becomes more complicated and refined.
Methods described in Japanese patent Application Laid-Open No. 2003-272998, Japanese patent Application Laid-Open No. 2004-304097 and Japanese patent Application Laid-Open No. 2005-354017 have the following concerns. Firstly, the concern is a point that an apparatus for working a mold becomes very expensive, and a capital investment increases because the mold is made from quartz. The concern is also a point that a process for forming the mold becomes complicated because the light-shielding film is provided on the projecting portion of the mold.